A typical data storage system or disc drive includes a rigid housing that encloses a variety of components. The components can include a storage medium, usually in the form of one or more discs, having data surfaces for storage of digital information. In general, multiple discs mounted on a spindle motor are called a disc stack. The spindle motor causes the disc(s) to spin and the data surfaces of the disc(s) to pass under aerodynamic bearing disc head sliders. The sliders carry transducers, which write information to and read information from the data surfaces of the disc(s). The sliders are supported by suspension assemblies, which in turn are supported by track accessing arms of an actuator mechanism. A voice coil motor rotates the actuator mechanism to position sliders relative to desired data tracks on the disc(s).
Airflow caused by the rotation of the discs causes airflow-induced vibrations of the disc(s), suspensions and track accessing arms. Airflow-induced vibration is a major obstacle in achieving higher track densities for the disc(s). Currently, track densities have reached a point where the combined effects of several airflow control devices are necessary to achieve desirable performance. Various airflow control devices, including air dams, flow diverters and disc separator plates have been used in disc drives to mitigate aerodynamic excitation. In most cases, however, these airflow control devices can affect performance criteria, such as power, reliability and shock performance.
Non-repeatable run-out (NRRO) measurements have shown that vibration levels observed on outer sliders (i.e. sliders positioned below or above a disc stack) in a disc drive are generally lower than those observed on inner sliders (i.e. sliders positioned between discs in a disc stack). The airflow around an outer slider is driven by the shearing action of a single disc surface, and is bounded by a zero-velocity non-slip boundary condition at the surface of the drive enclosure (top cover or base) opposite an outer disc surface. The flow around an inner slider, on the other hand, is driven by the shearing action of two disc surfaces and generally develops higher velocities, which leads to higher levels of aerodynamic excitation than those experienced by the outer sliders. In addition, a typical outer track accessing arm on an actuator mechanism supports a single suspension, whereas an inner track accessing arm on the actuator mechanism supports two suspensions. The structural dynamic coupling between the inner arm and two suspensions and the aerodynamic coupling between the inner suspensions results in higher response levels to aerodynamic excitation than the structural dynamic coupling between the outer arm and single suspension. Since lower levels of aerodynamic excitation are desirable to achieve high track densities, it is desirable to design a disc stack where all sliders experience the structural and aerodynamic conditions of outer sliders.
Embodiments of the present invention provide solutions to these and other problems, and offer other advantages over the prior art.